In the production of continuously threaded rod, studs, or similar helically formed parts, skewed-axis die rolling systems with two dies or three dies having regularly been used. The three-die configuration with three forming dies of the same diameter works well but requires an excessively complex gear box and a complicated and difficult to adjust die support frame. In addition, in a typical skewed axis system, the die diameter and, as a result, the bearings cannot be any larger than approximately five-and-one-half times the root diameter of the work; otherwise, they clash. Furthermore, the same diametral constraints require the mechanism for driving the three dies to be small in diameter, and therefore lacking in torsional strength and rigidity.
The two-die system permits the use of dies of unlimited diameter, within the confine of the machine, and therefore allows for more die regrinds, larger bearings, more robust spindles, and commensurately more rugged die drive mechanisms. In addition, the gear box and die mounting frames are less complicated and therefore less costly to build. However, when through-feed rolling continuously threaded bar, the part being formed has previously been held virtually on centers by input guide tubes, bushings, or a flat carbide work support blade. The tight fitting guide tubes must be changed for each rolling diameter, are difficult to set up, and do not effectively stabilize short, continuously threaded parts in the dies. Furthermore, when not very precisely set in line with the center lines of the dies, or too loose on the blank, they allow the start end of studs or long bars to dive or pop up. This results in deformation of the crests from contact with the input or output guide tubes or bushings, and heavy loads on the starting and finish reliefs of the dies which may accelerate wear and sometimes cause chipping. The use of a smooth carbide blade under the work to support it close to the line of the centers is generally simpler than the use of guide tubes or bushings, but the blades tend to wear and, when they are roughened by this wear, cause deformation of the crests of the part being formed. In addition, if set too low, wear accelerates and the crest deformation gets even worse. On the other hand, if set even slightly too high, the work pops out of the dies causing a possible smashup and other difficulties.
To remedy this situation, the use of a top and bottom blade has been attempted, but this restricts visibility and coolant flow and, with adequate clearances, produces a metastable rolling condition when the work is close to center. In addition, it is costly and difficult to set up and keep a desired adjustment.
All of these conditions are particularly aggravated when rolling stainless steel, hard materials, or other materials which tend to "pickup" on the blade or work support bushing. The present invention eliminates the difficulties involved in the use of guide bushings or flat blades when rolling such work on two-die systems and thereby gives them the rolling advantages of a three-die system without the commensurate disadvantages of high equipment cost, small diameter dies, and relatively weak spindles, bearings, and drives.